I have had my collection insured with a company that specializes in collectibles insurance for many years now. I would never - repeat never - insure my stuff under my standard homeowner's policy (with or without a rider). Companies like State Farm, Allstate etc just do not have a clue about collecting and collectibles and as others have said... you will have to run through major hoops to get a claim handled.
The company I use is:
https://www.collectinsure.com
They have been in business a long, long time and are based in Maryland. They are at Comic-Con almost every year. Their premiums are very reasonable and they PAY CLAIMS! They 100% specialize in insuring collectibles - so they "get it". My policy is currently underwritten by Lloyd's of London - can't get any more rock solid than that!
Here's some of the awesome things about their policies:
1) They insure for REPLACEMENT value! Amazing. You actually get paid what it would currently cost to replace your item
2) Their standard policy covers pretty much everything - including theft, fire and yes, earthquake (which is huge for me living in SoCal)!!!!!
3) You even get coverage for things being transported, mailed etc. The policies are very comprehensive.
4) They have very nice people who are excellent in customer service. When you call... you talk to a human.
5) You only need to itemize any item over $5,000. You do not need to continually send them lists of items etc. Basically, if you collect Sideshow Premium Format statues - you list them as just that. You don't need to list them individually (unless they're over $5k). The only updates you should make is if you begin collecting something totally new - like you begin to collect Prop replicas and you don't have that listed.
6) Adding coverage is simple and easy and can be done at any time. So if half way through the term year - you acquire $50,000 of stuff because you buy someone's whole collection - you can easily add coverage.
7) They automatically bump your collection value like 2-3% a year so the policy keeps up with standard appreciation.
Hope this helps someone out there.